Density Functional Theory Modeling of Low-Loss Electron Energy-Loss Spectroscopy in Wurtzite III-Nitride Ternary Alloys

Abstract

In the present work, the dielectric response of III-nitride semiconductors is studied using density functional theory (DFT) band structure calculations. The aim of this study is to improve our understanding of the features in the low-loss electron energy-loss spectra of ternary alloys, but the results are also relevant to optical and UV spectroscopy results. In addition, the dependence of the most remarkable features with composition is tested, i.e. applying Vegard's law to band gap and plasmon energy. For this purpose, three wurtzite ternary alloys, from the combination of binaries AlN, GaN, and InN, were simulated through a wide compositional range (i.e., Al x Ga1-x N, In x Al1-x N, and In x Ga1-x N, with x=[0,1]). For this DFT calculations, the standard tools found in Wien2k software were used. In order to improve the band structure description of these semiconductor compounds, the modified Becke-Johnson exchange-correlation potential was also used. Results from these calculations are presented, including band structure, density of states, and complex dielectric function for the whole compositional range. Larger, closer to experimental values, band gap energies are predicted using the novel potential, when compared with standard generalized gradient approximation. Moreover, a detailed analysis of the collective excitation features in the dielectric response reveals their compositional dependence, which sometimes departs from a linear behavior (bowing). Finally, an advantageous method for measuring the plasmon energy dependence from these calculations is explained.

Direct observation of spinodal decomposition phenomena in InAlN alloys during in-situ STEM heating

“…E p follows an approximately linear dependence with respect to the alloys’ compositional as observed experimentally In x Al 1−x N17 and calibrated according to calibrated according19, although to fully account for dependence, the usage of bowing parameter was suggested2728. VEELS SIs were recorded using a probe convergence semi-angle of 20 mrad, which delivered sub-Ångström resolution with 0.3 nA current, 0.025 eV/channel energy dispersion, a collection semi-angle of 12 mrad and 0.005 s dwell time for each pixel.…”

Reliable Characterization of Organic & Pharmaceutical Compounds with High Resolution Monochromated EEL Spectroscopy

“…From the CDF the ELF can be directly obtained. Figure 5 shows the ELF compared with the experimental low loss spectra [40]. The difference in relative intensity on the imaginary CDF caused form 2 to have broader peaks for low losses of energy.…”

Understanding the Anisotropy in the Electrical Conductivity of CuPtB-type Ordered GaInP Thin Films by Combining In Situ TEM Biasing and First Principles Calculations

“…Modified Becke–Johnson (mBJ) exchange potential was considered for the high symmetry ordered case. The relaxed structure was used to compute the energy loss function (ELF) and the complex dielectric function (CDF) by OPTIC − task of WIEN2k package. , The Perdew–Burke–Ernzerhof (PBE) functional was used setting RKmax to 7.0 and defining 500 k-points on the Brillouin zone. The energy and charge convergence criterion were set to 0.0001 Ry and 0.001 e, respectively.…”